Why Is My Period Blood Brown All Of A Sudden?

Should that be coming out of me, or...

Cassie Shortsleeve |
7 January 2019

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Photograph by Getty Images

Listen, you’re not exactly new to getting your period—by now, you know the ins and outs of your cycle (like how the cramps show up a day or two before it starts, or how you definitely need to keep some supers in your bag until at least day three).

But TBH, it still might freak you out a bit when that blood all of a sudden starts looking…brown.

First: Dial it back a bit—period blood can come in a range of different colours and consistencies and still be totally normal. But if you’re still kind of curious (and you know you are), here’s what’s really going on if your period blood looks a bit more brown than red.

So, what’s with the brown period blood?

Simply put: “Brown blood is just old blood,” explains Dr. Kari P. Braaten, an obstetric-gynaecologist at Brigham and Women’s Hospital in Boston, MA.

As the blood and tissue lining your uterus breaks down and leaves the body, it gets exposed to air. When that happens, the blood goes through a process called oxidation, which turns it brown—hence your brown period blood.

Often, you’ll find brown period blood at the very start of your cycle, when there might be a little bit of blood left over from your previous cycle, says Braaten. Other times, you’ll spot it at the very end of your cycle when your flow is on the lighter side. “In those cases, the blood sits around a bit or comes out more slowly, allowing time for it to oxidize and turn brown.” (Conversely, when blood is flowing faster and heavier, it’s more likely to be bright or dark red).

But, while oxidation is the most common culprit, it’s not the only reason you might be seeing brown blood. If you have consume a lot of iron—either from supplements or eating a lot of red meat or leafy vegetables—your period blood might skew brown. That’s because having more iron in your blood can enhance the oxidation process, says Dr. Dana Hunnes, a senior dietitian at Ronald Reagan-UCLA Medical Center.

Your hormonal birth control might also be to blame. Birth control options that contain no oestrogen (or low-dose oestrogen), can make the uterine lining less stable, which can lead to breakthrough bleeding during your cycle—and, because breakthrough bleeding is typically light, it can also appear brown, again, because of oxidation. But keep in mind, this too is totally normal when related to your menstrual cycle.

So, should I ever worry about brown period blood?

Most of the time, when brown period blood is linked to your menstrual cycle—like a few days before or after your period, or even breakthrough bleeding—it’s totally normal.

But when you start to see brown blood that isn’t related to your cycle, it can be cause for concern. Brown period blood outside of your typical cycle or after sex, for example, could be a sign of a yeast, bacterial, or sexually transmitted infections, or even an issue related to early pregnancy, like miscarriage or an ectopic pregnancy, says Dr. Pamela D. Berens, a professor of obstetrics, gynaecology, and reproductive sciences at McGovern Medical School at the University of Texas Health Science Center at Houston.

It may also be a sign of polycystic ovarian syndrome (PCOS), a hormonal disorder when your ovaries don’t regularly release an egg. PCOS also usually causes women to skip cycles for an extended period of time, allowing the uterine lining to grow increasingly thicker and unstable, which can then lead to irregular spotting or darker discharge between periods (a.k.a., brown discharge or blood), in addition to heavy, irregular bleeding.

If you’re worried about your period blood—or if that brown blood is not linked to your menstrual cycle (like, if it shows up totally unannounced)—it’s important to see your obstetric-gynaecologist, ASAP, to find out what’s going on.

But most of the time, noticing a little bit of brown—whether it’s because you’re nearing the end of your period (hallelujah!) or because you’re a green smoothie fanatic—that’s related to a regular cycle isn’t a sign of anything bad health-wise, confirms Braaten.

So, good news for you…but probably bad news for those new white undies you just bought.